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Implications of a palynological study in the Upper Precambrian from eastern Kasai and northwestern Shaba, Zaire
Author(s) -
Baudet D.
Publication year - 1987
Publication title -
geological journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.721
H-Index - 54
eISSN - 1099-1034
pISSN - 0072-1050
DOI - 10.1002/gj.3350220611
Subject(s) - riphean , geology , paleontology , precambrian , supergroup , palynology , biostratigraphy , radiometric dating , acritarch , borehole , outcrop , horizon , proterozoic , geometry , pollen , ecology , mathematics , biology , tectonics
This study presents the results of three borehole correlations in the Upper Precambrian Bushimay Supergroup, from the Kasai and Shaba provinces in Zaire. The most western borehole comes from the Lubi Valley (eastern Kasai) and cuts the lower part of the Bushimay Supergroup (BI). One palynological sample from the top of the BI Formation (BIe2) showed a microflora with Middle Riphean affinities that confirms the radiometric age previously found for the BI Formation in this area. The borehole in the Kanshi valley (eastern Kasai) located at about 30 km to the southeast of the Lubi valley, cuts the lower part of the BII Formation which consists of stromatolitic dolomites with black shaly horizons. A study of the systematics and the biostratigraphy of the microflora from the shaly horizons enables four different assemblages to be defined which correspond with the base of the Upper Riphean from Siberia, the North Atlantic area and Australia. The third borehole comes from Kafuku (Luembe valley, Shaba) located about 150 km to the southeast of the Kanshi core; it cuts detrital sedimentary rocks overlain by stromatolitic beds, respectively considered as BI and BIIa. An assemblage of acritarchs found in a shaly horizon from the upper part of the BI (BIe2) is comparable with the upper part of the BIIc horizon from Kanshi and consequently with those from the Upper Riphean. Thus, there is evidence of diachronism in the BI and BIIa‐c Formations from the North West to the South East in the Kasai‐Shaba area because the top of the detrital Formations and the stromatolites are younger towards the Kibaran continent. Consequently, the palaeogeographical model and the correlation scheme between Kasai and Shaba must be reconsidered. This diachronism combined with the classical scheme of a transgressive Upper Riphean sea on an eroding Kibaran continent, correlates with the transgressive cycle suggested by the vertical succession of the lithological facies of the supergroup. The age of the lavas in the supergroup needs to be reassessed.